Chain hoist



Aug 10 1926.. 1,595,823

c. DUNN ET AL CHAIN HOIST Filed Nov. 15 1921 2 Sheets-Sheet 1 WWII TIQJL- Amiga 1W 9 19260 C. KSUE EN ET AL CHAIN HOIST Filed Nov. 15 1921 2 SheetsSheet 2 lPhg N f EYE: E fiat 2. W Y %,JWL ZWZM Patented Aug. 10, 1926.

UNITED STATES PATENT QFFECE.

CHARLES DUNN AND ROBERT E. RISHELL, OF LOCK HAVEN, PENNSYLVANIA, AS-

SIGNORS TO CENTURY I-IOIST MANUFACTURING COMPANY, INCORPORATED, OF LOCK HAVEN, PENNSYLVANIA, A CORPORATION OF PENNSYLVANIA.

CHAIN HOIST.

Application filed November 15. 1921.

Our invention relates to so-called chain hoists for use in lifting heavy articles in machine shops and similar places, that is, hoists of the kind in which a plate cam, sometimes referred to as a snail, operates on a gear wheel which. in turn lifts the chain to which the load is attached, the plate cam being rotated by a sprocket wheel and end less chain. Chain hoists, as so constructed, have ordinarily had a hook on one end of the load chain, and the other end of the chain has been secured to the casing of the device and have been capable of operation only when the load is on a predetermined side of the load chain sprocket, so that the force applied by the load to the sprocket wheel produces a tendency to rotate in a predetermined direction only. The result of this construction is that the hoist can be used only to lift a load attached to the hook end of the load chain and that after the load has been raised, it is necessary to run the chain down by operation of the hand chain to lift the next succeeding load. The work of running down the hoist after each load or running it up in case succeeding loads are lowered, occupies considerable time and is a serious objection to the use of these hoists. To obviate this loss of time and to obtain certain other advantages, we place a hook on each end of the load chain so that when one book is up the other will be down and, therefore, it will not be necessary to run the hoist idly in the opposite direction after lifting or lowering the load. We also construct the operating mechanism so that it will be operable regardless of the direction of rotation in which the load tends to rotate the sprocket. This construction also makes it possible, by the use of a long lead chain or rope, to lift the load distances greater than the length of the load chain without blocking up the load. This has heretofore been impossible.

As will be readily understood by those skilled in the art, the application of the load to the opposite end of the load chain introduces a problem not heretofore present in hoists of this character, because in hoists as ordinarily constructed the hoist will run down if the attached end of the load chain is freed from the casing and the load applied thereto, or if a brake is employed a severe strain is placed on it; furthermore,

Serial No. 515,406.

the hoist would not be equally effective when lifting on one hook as when lifting on the other. Accordingly, we have provided a novel combination of gear wheel and plate care which are so constructed as to be equal ly effective regardless of which end of the chain carries the load, and which will not permit the load to run down under any circumstances.

This novel construction of a plate cam and gear wheel also has certain other ad vantages. It makes possible a single contact between the gear wheel and the tooth on the plate cam, except momentarily, and therefore reduces the friction between the moving parts, thus making the hoist easier to operate. It also makes it possible to do away altogether with a brake, thus greatly reducing the cost of construction and increasing its safety in operation.

The invention will be fully understood from the following description when taken in connection with the accompanying drawings, and the novel features thereof will be pointed out and clearly defined in the claims at the close of this specification.

In the drawings, Fig. 1 is a side elevation of a chain hoist embodying our invention, a portion thereof being in section to reveal the interior construction.

Fig. 2 is a section on line 22 of Fig. 1.

Fig. 3 is a detail showing the shape of the teeth, both on the plate cam and the gear.

Fig. 4 is a diagram showing the manner in which the teeth on the plate cam are constructed and the relation of the teeth to the teeth on the gear.

Fig. 5 is a diagram showing the relation between the working faces of a tooth on the gear.

Fig. 6 is a view illustrating the manner in which the hoist embodying our invention is used to lift a load for adistance greater than the length of the chain.

Referring now to the drawings, at 11 is shown the casing and at 13 is shown the hook by which the hoist is suspended or attached to some other member, as for instance a beam or cable. At 14 is shown the hand chain wheel and at 15 the hand chain. The hand chain wheel 14- is fast to the shaft 16 of a plate cam 17 which is provided with two cam members 18 and 19, which for convenience we call the cam teeth. The peculiar a rd:

novel structure of these teeth will be described in detail hereinafter. 'The two teeth 18 and 19 mesh with teeth formed on the edge of the gear 20. This gear is mounted on a stationary shaft 21 having its axis above the axis ofthe plate cam 17 and at right angles therewith. The construction and relationship of the teeth of the gear to the teeth on the plate cam will be more fully explained hereinafter.

On the side of the gear 20 is formed a sprocket wheel 22 over which theload chain 23 passes. This sprocket wheel is in the form of a hub containing chain pockets.

The ends of the load chain are both free for engagement with the load and are preferably provided with load hooks 24 and 25. In this respect our'hoist is different from chain hoists as heretofore constructed since they have had a hook at one end only and the other end of the load chain has been secured to the frame of the hoist. This construction is an importantfeature of our invention as it enables the hoist to be employed to lift loads for a distance greater than the length of the'load chain. For instance, if it is desired to lift the weight WV, (see Figure 6), by the hoist for a distance greater than that by which it can be accomplished by the length of the load chain of the chain hoist, as shown, which in the past has been impossible with chain hoists as heretofore constructed, the following procedure is adopted. The hook 24 is hooked into a link in the chain 27 at the point 3 Then the hook 24. is raised to its limit of movement by the rotation of the sprocket wheel 22 by means of the hand chain 15 in the ordinary way. 'lvhen the limit of movement of the load chain has been reached the hook '25 is then hooked into the chain 27 at the point 2, which is as low as possible, and the sprocket wheel 22 rotated in the opposite direction by the hand wheel. This lowers the load until it comes on the hook 25 when the hook 2 L can be unhooked from the chain 27. Thereafter the lifting of the load continues by means of the hook 24. The process can then be repeated, alternately engaging and disengaging the hooks 24: and 25 from the chain 27 and reversing the direction of rotation ofthe hoist. It will be seen that the load is always supported by one side of the load chain and that by providing a chain 27, or other suitable member of proper length, any length of lift may be obtained even with a hoist having a short load chain. It will also be seen that this is the result of employing a load chain, both ends of which are free forengagement with the load, and of having the hoist so constructed that it will operate with the load on either side of the load chain sprocket; This construction avoids the loss of time, expense of matei any given time.

rials and possible danger resulting from blockin up to take the load when the limit of the hoist has been reached, as has been necessary with hoists as at present constructed, as well as the loss of time due to running the hoist down or up idly.

The construction of the teeth on the plate cam 17 and on the gear 20 will now be described. This construction is an important feature of our invention, because by making the teeth on the plate cam in the manner to -be described, it is possible to produce a hoist which is operable equally well with the load applied on either side of the load chain sprocket.

Only-two teeth 18 and 19 on the plate cam are employed and the construction is such that, except momentarily, only one tooth is in contact with the gear teeth at This is important because it reduces the friction between the teeth on the plate cam and the teeth on the gear wheel to a minimum and consequently makes the device much easier to operate. The construction of each of the two teeth 18, 19 is identical, therefore only one will be described. The outside working faces of the teeth are portions of involute curves which are conveniently termed the pitch lines of the teeth. 'These involute curves are formed on a base circle 28, the radius of which is substantially twice the circular pitch of the gear divided by pi. By circular pitch, we mean the distance measured on the pitch circle between the center lines of two adjacent teeth of the gear wheel, this distance being indicated at c on Figure 1. Starting at any convenient point of origin on the base circle, as for instance at d, the involute curve is traced by drawing tangents e to the base circle and laying out on these tangents the successive circumferential distances measured from the origin. 'lVhen the pitch line has thus been fixed, the position of the side edge of the tooth is determined by laying off equal distances on the several tangents, these distances being laid off inwardly from the pitch line of the tooth. The sides of the teeth, by which is meant the curves formed by a cross section taken on any tangent to the base circle, as for instance the line h.h in Figure 4, are cycloidal; that is, the edges of the cross section are cycloidal and the cross section as a whole has the appearance of a cycloidal gear tooth, as shown in Figure 3. The cycloid forming the working faces of the teeth is formed by revolving the pitch circle of the gear on the straight line which is formed by the face of the cam when viewed edgewise.

The edges of the teeth on the gear wheel, when viewed edgewise, are arcs of circles, the centers of which are on the centerline of the face of the gear. This center line is marked jlc in Figure 4 and the edges of the gear teeth are indicated by the lines Zm and a0 respectively. The outer edge Zm is formed on a radius such that the edge of the tooth will have greater curvature, that is, it will be more curved than the corresponding portion of the involute edge of the tooth on the plate cam. This construction is necessary so that there will be only a single point of contact between the respective teeth. Likewise the edge n0 is the arc of a circle whose center is located on center line j-Ja, but this are has a less curvature than the corresponding portion of the involute edge of the tooth on-the plate cam so that there will be contact at one point only. This construction is of importance because the opposite sides of the teeth both on the plate cam and on the gear wheel are effective when the load is changed from one side of the sprocket wheel to the other. The point of contact between the gear tooth and the cam tooth is not on the center line of the gear face but at a distance from it, this distance being determined by the shape of the involute which is itself determined by the size of the base circle. The choice of the size of the base circle and the distance which the center line j lies at one side of the axis of the plate cam, this distance being marked rs in Figure a, controls the position of this point.

In practice, the size of the base circle will be such that the angle between the force normal, which is a line perpendicular to a common tangent at the point of contact, and the center line will be less than the coefiicient of friction angle of the materials to be employed, since if the angle is greater the force exerted by the gear tooth on the plate cam will tend to rotate the plate cam and thus make the hoist run down.

In practice, where the gear is made of steel and the plate cam is made of bronze, this angle will be about 2, since the coefficient of friction angle of steel and bronze is about 3 12. We have found that, if the radius of the base circle is made substantially equal. to the circular pitch of the gear divided by pi, the conditions will be fulfilled.

YVhen constructed as described, the hoist is reversible and can be operated in either direct-ion. The maximum load can be placed on either hook and the plate cam left in any angular position, but the force exerted by the load cannot overcome the standing friction and therefore cannot start the rotation of the plate cam. On the other hand since only one of the teeth on the plate cam is in contact with the teeth on the gear at any given time, except momentarily, when the point of contact between the gear and the cam teeth passes from one to the other of the cam teeth, the friction is reduced to a minimum and consequently the hoist can be easily operated.

iVhat we claim is c 1. A hoist comprising a face cam and a gear, the axis of said cam being parallel to the gear but not passing through the center of the gear, said cam being provided with teeth in the form of involutes, and said gear having teeth on the edge, the edges of the teeth being curves, one curve having a curvature greater than that of the face of the involute tooth with which it contacts, and the other curve being of less curvature than the opposite face of the involute.

2. A chain hoist comprising a gear hav ing teeth on its periphery and a plate cam having two teeth in the form of involutes the ends of which overlap slightly, the corresponding edges of the gear teeth being of like curves, the curves of one of the corresponding edges being of a curvature greater than the face of the involute teeth with which they contact and the curves of the other corresponding edges being of a curvature less than the face of the involute teeth with which they contact, said gear and plate cam being so constructed and arranged that, except momentarily, there will be contact at a single point between one of the curved edges of one of said gear teeth and one of the faces of one of said involute teeth.

In testimony whereof we affix our signatures'.

CHARLES DUNN. ROBERT H. -RISHELL. 

